You may know this by now, but, in order to sew you won’t just be sewing straight seams.
If a straight seam is the “easiest” to sew, then the second easiest to sew would be sewing two curved pieces together when the two curves are exactly the same.
You’ll encounter same-curve seams in neck or armhole facings, contoured waistbands, crotch curve in pants, flaps for pockets or pouches, and some collars (among other things).
The trick to successfully sewing a curve is to guide the fabric under the foot and through the needle without distorting the fabric.
Let the feed dogs do their job. But, remember they want to pull the fabric straight through the machine. So, you need to train your hands to help make the curve.
This is MUCH easier done on stable fabrics than it is on “unstable” fabrics such as chiffon, charmeuse satin, and super lightweight knits.
Keep in mind that the seam allowance is the distance from the edge of the fabric to the needle.
As you sew, the most important thing to keep “right” is the seam allowance at the needle. This may mean that the seam allowance will be “wrong” before and after the needle. (It’s geometry).
Don’t try to make it “right” longer than the geometry of the curve allows. That is, don’t try to make the seam straight to sew it. Work with the curve.
This is more difficult to do on tighter curves.
Here’s a short video that explains what I tried to type.